The present invention relates to a printed circuit board and its manufacturing method. More particularly, the present invention relates to a so-called composite printed circuit board which comprises resin substrates laminated on a ceramic substrate and also relates to a manufacturing method of the composite printed circuit board.
A so-called composite printed circuit board, comprising resin substrates laminated on a ceramic substrate, is conventionally known as a printed circuit board which is capable of assuring excellent heat radiation and other thermal properties as well as realizing high-density electric component mounting.
The composite printed circuit board is manufactured in the following manner.
First, a uncured state heat-hardening resin (e.g., a polyimide resin or the like) is coated on a ceramic member (i.e., a ceramic substrate) on which a printed conductor pattern and a printed resistor are formed. Next, a laser beam is applied to a predetermined portion on a heat-hardening resin layer to open a via-hole so as to extend across this resin layer. Then, a conductor pattern and a via are formed on or in the heat-hardening resin layer by plating or sputtering.
When a plurality of resin substrates are laminated, another uncured state heat-hardening resin is coated on the hardened heat-hardening resin. Then, the above-described processes are repeated to obtain a composite printed circuit board having a desired number of resin layers.
However, the above-described conventional technique requires a large number of manufacturing processes starting from the step of coating the uncured state heat-hardening resin on the ceramic substrate to the step of forming the conductor pattern and the via. When the required number of layers constituting the composite printed circuit board is large, similar steps must be repeated to build up the layers. The manufacturing processes become very complicate.
In view of the foregoing problems of the prior art, the present invention has an object to provide a printed circuit board and its manufacturing method which is capable of simplifying manufacturing processes even if a large number of resin layers are laminated on a ceramic substrate.
In order to accomplish the above and other related objects, the present invention provides a printed circuit board comprising a ceramic substrate and a resin base layer integrally laminated on said ceramic substrate, wherein the resin base layer is formed by pressing and heating a laminated body consisting of a conductor pattern forming film and said ceramic substrate, and the conductor pattern forming film includes a resin film made of a thermoplastic resin and a conductor pattern formed on a surface of said resin film.
According to this arrangement, the resin base layer is formed by the resin film made of a thermoplastic resin. The resin film and the ceramic substrate are pressed and heated together to obtain the resin base layer formed integrally on the ceramic substrate.
The required processing time can be reduced. When a plurality of layers are laminated, these layers are bonded at a time by heating and pressing them together. Thus, the present invention simplifies the manufacturing processes of a printed circuit board.
According to the printed circuit board of the present invention, it is preferable that the thermoplastic resin has an elastic coefficient in a range of 1xcx9c1,000 MPa in a temperature level during the heat and press treatment.
According to this arrangement, the resin film and the ceramic substrate can be surely bonded together by performing the press treatment under the condition that the elastic coefficient of resin film is sufficiently lowered to the range of 1xcx9c1,000 MPa.
More specifically, it is preferable that the conductor pattern forming film is a single-sided conductor pattern film having the conductor pattern formed on only one surface of the resin film.
According to this arrangement, when a plurality of conductor pattern forming films are laminated, it is not necessary to prepare and process a plurality of different kinds of conductor pattern forming films. The manufacturing processes can be further simplified.
Furthermore, it is preferable that the ceramic substrate comprises a printed conductor pattern and a printed electric element which are connected to each other and formed on a surface the ceramic substrate to which the conductor pattern forming film is bonded, the printed conductor pattern being formed by printing a conductor forming paste and then sintering the conductor forming paste while the printed electric element being formed by printing an electric element forming paste so as to be connected to the conductor forming paste and then sintering the electric element forming paste, and the printed conductor pattern is connected to the conductor pattern formed on the resin film via an electrically conductive paste which is filled in a via-hole extending across the resin film.
This arrangement makes it possible to embed the printed electric element along a bonding surface between the ceramic substrate and the conductor pattern forming film. It is, hence, possible to reduce the total number of electric elements to be mounted on the outermost surface of the printed circuit board. This leads to the downsizing of the printed circuit board.
Furthermore, it is preferable that the ceramic substrate comprises only a printed electric element formed on a surface to which the conductor pattern forming film is bonded, the printed electric element being formed by printing an electric element forming paste and then sintering the electric element forming paste, and the printed electric element is connected to the conductor pattern formed on the resin film via an electrically conductive paste which is filled in a via-hole extending across the resin film.
This arrangement makes it possible to embed the printed electric element along a bonding surface between the ceramic substrate and the conductor pattern forming film. It is, hence, possible to reduce the total number of electric elements to be mounted on the outermost surface of the printed circuit board. This leads to the downsizing of the printed circuit board. In addition, there is no necessity of forming the printed conductor pattern on the surface of the ceramic substrate on which the conductor pattern forming film is bonded. The manufacturing processes can be further simplified.
The present invention provides a method for manufacturing a printed circuit board. In a laminating step, a conductor pattern forming film and a ceramic substrate are laminated. The conductor pattern forming film includes a resin film made of a thermoplastic resin and a conductor pattern formed on a surface of the resin film. In a bonding step, the conductor pattern forming film and the ceramic substrate are bonded by heating and pressing from both sides of a laminated body of the conductor pattern forming film and the ceramic substrate, thereby obtaining a resin base layer integrally laminated on the ceramic substrate.
The manufacturing method of this invention makes it possible to reduce the required processing time. When a plurality of layers are laminated, these layers are bonded at a time by heating and pressing them together. Thus, the present invention simplifies the manufacturing processes of a printed circuit board.
Furthermore, it is preferable that the conductor pattern contains at least one metal component and the bonding step is performed at a temperature level not lower than 250xc2x0 C. where the elastic coefficient of the thermoplastic resin constituting the resin film is in a range of 1xcx9c1,000 MPa.
According to this manufacturing method, the resin film and the ceramic substrate can be surely bonded together in the bonding step by performing the press treatment under the condition that the elastic coefficient of resin film is sufficiently lowered to the range of 1xcx9c1,000 MPa. Furthermore, increasing the temperature to 250xc2x0 C. or above is effective to improve the surface activity of the metal component contained in the conductor pattern. Hence, the conductor pattern and the resin film are surely bonded together when the conductor pattern is pressed against the resin film which has a sufficiently lowered elastic coefficient.
More specifically, it is preferable that the conductor pattern forming film is a single-sided conductor pattern film having the conductor pattern formed on only one surface of the resin film.
According to this arrangement, when a plurality of conductor pattern forming films are laminated, it is not necessary to prepare and process a plurality of different kinds of conductor pattern forming films. The manufacturing processes can be further simplified.
Furthermore, it is preferable that the manufacturing method for a printed circuit board further comprises the following steps.
In printed conductor pattern forming step, a printed conductor pattern is formed before performing the laminating step. The printed conductor pattern is formed by printing a conductor forming paste on a surface of the ceramic substrate on which the conductor pattern forming film is bonded in the bonding step and then by sintering the conductor forming paste. In a printed electric element forming step, a printed electric element is formed before performing the laminating step. The printed electric element is formed by printing an electric element forming paste so as to be connected to the conductor forming paste on a surface of the ceramic substrate on which the conductor pattern forming film is bonded in the bonding step and then by sintering the electric element forming paste. And, in a filling step, an electrically conductive paste is charged into an end-closed via-hole before performing the laminating step. The end-closed via-hole extends across the conductor pattern forming film and has a bottom defined by the conductor pattern formed on the conductor pattern forming film.
Then, through the bonding step, the electrically conductive paste filled in the end-closed via-hole provides an electric connection between the conductor pattern formed on the conductor pattern forming film and the printed conductor pattern formed on the ceramic substrate.
This manufacturing method makes it possible embed the printed electric element along a bonding surface between the ceramic substrate and the conductor pattern forming film. It is, hence, possible to reduce the total number of electric elements to be mounted on the outermost surface of the printed circuit board. This leads to the downsizing of the printed circuit board.
Alternatively, it is preferable that the manufacturing method for a printed circuit board further comprises the following steps. In a printed electric element forming step, a printed electric element is formed before performing the laminating step. The printed electric element is formed by printing an electric element forming paste on a surface of the ceramic substrate on which the conductor pattern forming film is bonded in the bonding step and then by sintering the electric element forming paste. And, in a filling step, an electrically conductive paste is charged into an end-closed via-hole before performing the laminating step. The end-closed via-hole extends across the conductor pattern forming film and has a bottom defined by the conductor pattern formed on the conductor pattern forming film.
Then, through the bonding step, the electrically conductive paste filled in the end-closed via-hole provides an electric connection between the conductor pattern formed on the conductor pattern forming film and the printed conductor pattern formed on the ceramic substrate.
This manufacturing method makes it possible to embed the printed electric element along a bonding surface between the ceramic substrate and the conductor pattern forming film. It is, hence, possible to reduce the total number of electric elements to be mounted on the outermost surface of the printed circuit board. This leads to the downsizing of the printed circuit board. In addition, there is no necessity of forming the printed conductor pattern on the surface of the ceramic substrate on which the conductor pattern forming film is bonded. The manufacturing processes can be further simplified.